Inhibiting polymer precipitation in acetylene purification process



United States Patent acetylene-bearing gas is generally purified by treating it with a selective solvent whereby substantially all the acetylene as well as the higheracetylenes are absorbed,

while the less soluble components pass off in the oif-gas stream. The resultant solution of acetylenes is then treated to separate acetylene from the higher acetylenes and both from the solvent, the solvent then being recycled. Various solvents have been proposed and eifectively employed in this purification system, one of the preferred being butyrolactone.

Although this purification system has been commercially employed to a considerable extent, it suffers from one serious disadvantage. Because of the presence of higher acetylenes in the reaction gas and the use of elevated temperatures in the purification system, polymer formation occurs. Polymer thus formed builds up in the solvent and tends to precipitate particularly in the presence of water. Resultant. accumulations of polymer solids in the heat exchangers, stripping columns, lines and the like necessitate periodic shutdowns of equipment thus seriously limiting production.

One suggested method of minimizing the polymer content of the solvent is to treat a continuously withdrawn small slip stream of stripped solvent with water to precipitate polymer which can then be separated by filtration prior to recycling of the solvent. This is not wholly satisfactory because of filtration problems caused by the fine size of the polymer. In addition, the problem of polymer precipitation within the purification system is aggravated because of the possibility of introducing additional water into the solvent. It also has been proposed to combat this problem by adding any of various chemical agents to the solvent believed to be capable Patented Oct. 6, 1959 inhibiting the problem of polymer formation in the purification of acetylene. Particularly, therehas been a continued need for reducing the frequency of shutdowns of the purification system for cleaning necessitated by the accumulation of precipitated polymer.

accordance with this invention, theseneeds are met to amost'unusual and unexpected degree. It now has been found that the precipitation of polymer can be greatly inhibited by incorporating in the, solvent a compoundof the formula v wherein R and R are H or alkyl radicals of l-4 carbon atoms. In contrast to the previous use of chemical addition agents which are alleged to overcome the polymerization problem by stabilizing the solution, the agents of this invention do not reduce polymerization but appear to inhibit the precipitation of solids by forming a polymer considerably more soluble in a selective solvent or solvent-water system than heietofore obtained. At any rate, regardless of how it functions, the precipitation and accumulation of solids in the acetylene purification system is substantially reduced by the presence in the system of an inhibitor according to this invention.

The amount of inhibitor employed may be quite Widely varied. Precipitation of polymer has been considerably inhibited in a solution containing as little as 0.01% by weight of inhibitor. Generally, the amount of inhibitor will be greater than this and may range to as high as 5% or more, although little added advantage appears to be gained by using these higher amounts. Usually, therefore, the amount of inhibitor will be less ranging from about 0.1% to about 1.0%.

To avoid a build up of soluble polymer in the solvent, a continuous slip stream of stripped solvent may be withdrawn and treated by any means which form no part of this invention to separate the polymer.

The following examples further illustrate the invention. Unless otherwise noted, all parts are by weight.

EXAMPLE 1 Samples comprising 50 parts of water, 50 parts butyrolactone, 0.25 part diacetylene and each containing an inhibitor according to Table I are placed in sealed tubes and heated for 16 hours at 125 C. Two additional samples, sample 1 containing no inhibitor and sample 2 containing no inhibitor and no diacetylene are used as blanks and similarly treated. Each sample is then observed for polymer precipitation.

Table 1 Sample N o. Inhibitor Pyridine. 1.0 0.1 0. 01 2-methyl-5-ethyl pyridine 1. 0 z-pimlina 3-picoline- 4-plc0line- Polymer precipitation after 16 hours Yes N o N o N o Slight N 0 EXAMPLE 2 of stabilizing the solution of higher acetylenes against polymerization. Although numerous materials have been proposed, none has been foundto be particularly efiective in reducing polymer formation.

There has continued to remain, therefore, a need for Thereaction gas from a partial oxidation of methane is bubbled through butyrolactone at C. and at a rate of 0.5 c.f.h. After 24 hours, the butyrolactone is mixed with 4 volumes of water. Solids are precipitated,

- EXAMPLE3 The procedure of Example 2 is followed except that the solvent contains 1.0% Z-ethyl-S-methyl pyridine ,On

the addition of water totheisolvent after 2 4'hou rs, Th0

solids are precipitated.

Similar results are obtained using other inhibitors in varying amounts in accordance with this invention. 'Bolymer precipitation is also inhibited in a similar-"manner when using selective solvents other than butyrolactoii'e, We claimi 1. The method of inhibiting polyrn'er precipitation in the preparation of acetylene in which an acetylene bea'b,

ing gas is treated with butyrolactone wherebfacet'ylene" and higher acetylenes are absorbed which comprises carrying out the absorption in the presence of a compound 15 of the formula References Qited in the'file of this patent rurrzn STATES PATENTS 1,924,979 Carma et a1. Aug. 29, 1933 2,715,102 Nelson Aug. 9,1955 2,715,104 Nelson Aug. 9, 1955 

1. THE METHOD OF INHIBITING POLYMER PRECIPITATION IN THE PREPARATION OF ACETYLENE IN WHICH AN ACETYLENE-BEARING GAS IN TREATED WITH BUTYROLACONE WHEREBY ACETYLENE AND HIGHER ACETYLENES ARE ABSORBED WHICH COMPRISES CARRYING OUT THE ABSORPTION IN THE PRESENCE OF A COMPOUND OF THE FORMULA 